During the production and use of equipment for the automatic cleaning of inking rollers and rubber-coated cylinders of printing machines, described in Italian Patent No. 1,286,206 (or equivalent EP 0 916 492), it was found to be useful to make certain important modifications to improve the operation of the means of supplying the fluid mixture for cleaning the said rollers and cylinders, and in particular to provide a uniform distribution to the different supply holes of the said mixture formed from pressurized air and liquid, with small percentages of the liquid dispersed in the air which acts as the means of transport. For a clearer understanding of the objects of the invention, it will be useful to recall the prior art described in the patent cited above, with reference to FIG. 1 of the attached drawings, which shows a cross section of the fluid mixture supply bar, and with reference to FIGS. 2 and 2a which show, in a plan view from above and divided into two parts, with the division along the mid-line, the bar of FIG. 1 with the channels which distribute the cleaning fluid mixture to the various supply nozzles of the bar. The equipment which is referred to (FIG. 1) comprises a bar 1 of light alloy, parallel to, and located at a short distance from, each rubber-coated cylinder 2, and having on its side facing the cylinder a longitudinal rectilinear recess 3 in which a presser 4 with an elastic and yielding membrane 5 is guided. The said bar 1 houses the pneumatic actuators 6 which on command push the presser 4, 5 against the cylinder 2, to bring into contact with the cylinder the interposed cloth 7 on which a cleaning fluid has been previously sprayed by means of nozzles 9 mounted in one or more seats 8 formed in the said side of the bar which faces the cloth, these nozzles being connected, by means of holes 10, to channels 1000 formed by milling in a flat side of the said bar, over which a flat seal 12 is subsequently extended and a cover plate 13 is fixed with screws 14 to convert the said channels into ducts. These channels are connected symmetrically to other supply channels branching from each other, which are bifurcated and progressively reduced in number, until they meet a single fluid mixture supply duct 100, connected to an aperture 15 at one end of the bar 1 (see also FIGS. 2, 2a). Each bifurcation of the said channels is essentially Y-shaped and is formed as part of a rectilinear path, and the channels resulting from the bifurcation are structured in such a way as to offer an essentially equal resistance to the passage of the fluid mixture, so that this fluid is divided into essentially equal quantities in each bifurcation. The number of bifurcations is such that each final channel resulting from a bifurcation supplies a single nozzle, in such a way as to provide a balanced distribution of the cleaning fluid mixture between the various nozzles of the equipment. FIGS. 2 and 2a also show that the aperture 15 communicates through the perpendicular hole 16 with a first channel 100 formed longitudinally in the bar 1 and that this channel is subjected, before the mid-line 18 of the bar, to a bifurcation B1 which gives rise to two rectilinear and opposing ducts 101, 201 which, before reaching the half-way point of each half bar, are subjected to respective bifurcations B2, B3 which give rise to respective pairs of ducts, aligned with and identical to each other, 102, 202 and 103, 203, which are then subjected to respective bifurcations B4, 85 and B6, B7 which give rise to pairs of ducts 104, 204, 105, 205 and 106, 206, 107, 207 which then undergo respective and final bifurcations B8, B9, B10, B11 and B12, 813, 814, B15 which, by means of their respective channels 108, 208, 109, 209, 110, 210, 111, 211, 112, 212, 113, 213, 114, 214, 115, 215, supply the holes 10 to which respective nozzles 9 are connected. Each channel is followed by two initially rectilinear channels, which are located a short distance apart from each other, are parallel, and are equidistant from the upstream channel. The common dividing wall by which the channels resulting from each bifurcation are connected to the upstream channel is V-shaped in plan and has a sharp point. The two branches following each bifurcation open and proceed in opposite directions, one along an S-shaped path and one along a U-shaped path, as shown in the attached drawings. The number 26 indicates rectilinear milled grooves formed in the base of the channel 11 containing the cleaning liquid transport channels, blind threaded holes being formed in these milled grooves for interaction with the screws 14 for securing the cover assembly 12, 13 which completes the said channels according to the prior art (FIG. 1).
To balance the pressure drops, the channels resulting from each bifurcation are made with a suitable depth and width, as shown in FIG. 1. For example, in the bar made by the applicant and illustrated in FIGS. 2 and 2a, provided with sixteen supply nozzles, the initial channel 100 has a depth of approximately 10 mm and a width of approximately 5 mm, while the branches of the final bifurcations have a width of approximately 3 mm and a depth of approximately 2.5 mm. In the same bar, shown in FIGS. 2 and 2a, the initial ducts have, for example, a width of 4 mm and a depth of 8 mm. After the first bifurcation, the width changes to 3 mm and the depth to 6 mm. After the next bifurcation, the depth remains constant and the width decreases to 2 mm. The final bifurcation has branches 2.5 mm deep and this depth and the width of 2 mm remain unchanged up to the end.
In the bar in question, the cleaning liquid is injected in a low proportion in a flow of pressurized air which has the function of transporting the liquid and by means of which the liquid is supplied to the aperture 15 of the bar. FIGS. 2 and 2a clearly show that the cleaning fluid mixture transport circuit has many curves. The low concentration of the cleaning fluid in the transporting air flow has the effect of making the mixture of air and liquid tend to break up and lose its homogeneity during its passage around each curve of the said circuit, as a result of the centrifugal force, gravity, and especially the contact with the walls of the ducts, on which the liquid tends to be deposited.
At the exit from each curve of the mixture transport duct, it is possible for the quantity of liquid deposited on one lateral wall of the duct to be very different from that deposited on the opposite lateral wall. If the rectilinear duct which follows the curve has a limited length, the mixture of air and liquid cannot be re-compacted and made uniform before it reaches the next bifurcation, and therefore the division of the mixture into the two channels of the said bifurcation may take place incorrectly, in the sense that more liquid than air, or vice versa, may reach one channel.
This disadvantage can be particularly marked in the final bifurcations of the circuit shown in FIGS. 2, 2a, for example those indicated by B9, B10 and B13, B14, since the cross section of the channels of the circuit decreases progressively towards the end, for example down to the aforesaid value of 2xc3x972.5 mm. Although the progressive reduction of the section of the channels enables the mixture to be concentrated towards the centre of the channels so that it can be branched in equal portions in the next bifurcations, it also introduces considerable pressure drops into the circuit, and these progressively limit the quantity of air reaching the nozzles, with a negative effect on the desired uniformity of spraying of the mixture by all the nozzles of the bar.
To this disadvantage must be added the fact that the limited cross section of the final channels of the circuit can be decreased incidentally by the deformation of the elastomeric seal 12, under the pressure of the plate 13, in these channels.
The invention is intended to overcome these and other disadvantages of the known art with the following idea for a solution. Upstream from each bifurcation, preferably at the branching point of the bifurcation, a localized restriction which is symmetrical in plan is introduced, and this has the function of compacting the mixture on the mid-line of the point of the said bifurcation, in such a way that the mixture can be distributed equally in the two following channels. The use of the said restrictions makes it possible to form the transport channels 1000 of the bar with sections which can differ only slightly from the start to the end, thus limiting the loss of flow of the whole circuit, while these restrictions, by the progressive decrease of their size from the start to the end, also have the effect of progressively increasing the pressures in the mixture transport circuit, so that a mixture formed from the same quantity of liquid and air reaches the various outlet nozzles 10 in a quantity and at a pressure sufficient to ensure the perfect spraying of the liquid.